The only time I nickname them is for a challenge - a nuzlocke or a solo or such. When I do, I mostly use relatively common names that just seem appropriate for whatever reason. In a normal game, I never nickname them. And aside from trading nice stuff out of a game so that I can restart it, I've never traded between games, and have never traded between gens at all. I like to go into each game completely fresh and just go out into that region and make do with whatever I can catch there.